Problem: If $5a + 6b = 1$ and $2x + 3y + z = 4$, what is $45a + 54b - 4z - 12y - 8x$ ?
Explanation: $= 45a + 54b - 8x - 12y - 4z$ $= (9) \cdot (5a + 6b) + (-4) \cdot (2x + 3y + z)$ $= (9) \cdot (1) + (-4) \cdot (4)$ $= 9 - 16$ $= -7$